CVE-2025-11385 identifies a buffer overflow vulnerability in the Tenda AC20 router firmware versions up to 16.03.08.12. The flaw exists in the sscanf function within the /goform/fast_setting_wifi_set endpoint, where the timeZone parameter is improperly validated, allowing an attacker to overflow the buffer. This vulnerability is remotely exploitable without requiring authentication or user interaction, making it highly accessible to attackers. Exploitation could lead to arbitrary code execution, enabling attackers to take full control of the device, or cause denial of service by crashing the router. The vulnerability has a CVSS 4.0 base score of 8.7, indicating high severity due to its network attack vector, low complexity, and high impact on confidentiality, integrity, and availability. Although no confirmed exploits are currently active in the wild, the public disclosure of the exploit code increases the likelihood of imminent attacks. The vulnerability affects multiple firmware versions from 16.03.08.0 through 16.03.08.12, necessitating urgent patching or mitigation. The Tenda AC20 is commonly deployed in small to medium enterprise and home networks, making this a significant risk for network infrastructure compromise.

For European organizations, exploitation of this vulnerability could lead to unauthorized access to internal networks, interception or manipulation of sensitive data, and disruption of network services. Compromise of routers can serve as a foothold for lateral movement within corporate networks or as a launchpad for further attacks such as data exfiltration or ransomware deployment. The loss of router availability could disrupt business operations, especially for organizations relying on Tenda AC20 devices for critical connectivity. The confidentiality and integrity of communications passing through these routers are at risk, potentially exposing private or regulated information. Given the remote and unauthenticated nature of the exploit, attackers can target vulnerable devices at scale, increasing the threat to European enterprises, especially those with less mature network security practices or delayed patch management. The impact extends to residential users as well, potentially affecting remote workers and home office setups.

Organizations should immediately identify and inventory all Tenda AC20 devices running affected firmware versions. The primary mitigation is to apply firmware updates from Tenda once available; if no official patch exists yet, organizations should consider temporary measures such as disabling remote management interfaces and restricting access to the /goform/fast_setting_wifi_set endpoint via firewall rules. Network segmentation should isolate vulnerable devices from critical assets to limit potential lateral movement. Continuous monitoring for anomalous traffic targeting the vulnerable endpoint can help detect exploitation attempts early. Employing intrusion detection/prevention systems (IDS/IPS) with signatures for this vulnerability can provide additional defense. Organizations should also enforce strict network access controls and consider replacing outdated or unsupported devices. User awareness campaigns can help ensure that home users and remote workers understand the risks and update their devices promptly.